"World civilization has created an ecological crisis without any precedent in all of human history," Mr. Gore said at a Monitor breakfast this week. But the natural leader of the world, the United States, is "stonewalling" as the rest of the world negotiates how to avert disaster. "Every major leader in the entire world is going to the earth summit in Brazil except George Bush," Gore said.

Other countries have agreed on a long list of measures and accords addressing matters from preventing global warming to a permanent ban on the dumping of nuclear waste into the oceans. "If the world misses this opportunity ... then the prospects for preventing an ecological catastrophe are significantly diminished," the senator said.

Bush and his aides counter that the US has in fact been a world leader in environmental safeguards and cleanup, and should not take any action that might slow economic recovery.

The main issue in contention is limiting emissions of "greenhouse" gases that trap heat in the atmosphere, thought to cause a slow global warming. The US is the largest emitter of carbon dioxide, a major greenhouse gas.

Most other nations are prepared to agree to goals and timetables for limiting such gases. But the White House argues that such timetables are too simplistic. Actions should "fit each nation's particular circumstances," President Bush said in a recent statement.

The White House still has not yet announced whether the president will attend the Rio summit.